The study of urban aerosol and its influence on radiation and meteorological regime is important due to the climate effect. Using COSMO-ART model with TERRA_URB parameterization, we estimated aerosols and their radiative and temperature response at different emission levels in Moscow. Mean urban aerosol optical depth (AOD) was about 0.029 comprising 20-30% of the total AOD. Urban black carbon mass concentration and urban PM10 accounted for 86% and 74% of their total amount, respectively. The urban AOD provided negative shortwave effective radiative forcing (ERF) of -0.9 W m(-2) at the top of the atmosphere (TOA) for weakly absorbing aerosol and positive ERF for highly absorbing aerosol. Urban canopy effects decreased surface albedo from 19.1% to 16.9%, which resulted in positive shortwave ERF at TOA, while for longwave irradiance negative ERF was observed due to additional emitting of urban heat. Air temperature at 2 m decreased independently on the ERF sign, partially compensating (up to 0.5 degrees C) for urban heat island effect (1.5 degrees C) during daytime. Mean radiative atmospheric absorption over the Moscow center in clear sky conditions reaches 4 W m(-2) due to urban AOD. The study highlights the role of urban aerosol and its radiative and temperature effects.

We compute the effective radiative forcing (ERF) of the internally mixed sulfate-black carbon (SBC) aerosol species in the Geophysical Fluid Dynamics Laboratory's (GFDL) Atmospheric Model version 4 (AM4) model using five different formulations. The formulations differ in how they account for the presence of other aerosol species. The global mean ERF of SBC in the GFDL AM4 model ranges from -0.51 +/- 0.1 to -1.06 +/- 0.1 W m-2. The three most realistic configurations of the five, in which the emissions of other aerosol species vary between 1850 and 2010 states, depict a tighter distribution of ERF (-0.51, -0.55, and -0.57 +/- 0.1). The two outlier configurations completely exclude one or more other aerosol species, which is slightly unrealistic but included for completeness. The former three configurations, however, result in substantially different ERFs over the regional hot spots of aerosols, e.g., over the land-mass of East China; the choice of the emission conditions for organic carbon (i.e., present-day or preindustrial) affects the ERF of SBC by similar to 37%. The component of ERF related to aerosol-cloud interactions (ACI) gets principally affected by the presence of other aerosol species. The higher the emissions of other aerosol species, the lesser is the ERF of SBC associated with ACI. This finding suggests that for ERF estimates, the choice of the emission level/concentrations of the other aerosol species significantly affects the estimates of SBC, especially over the aerosol hot spots. The radiative imbalance at the top-of-the-atmosphere caused by the changes in the anthropogenic emissions of aerosols from preindustrial (PI) times to the present-day (PD), with the oceanic conditions held constant, is termed as the effective radiative forcing (ERF) of anthropogenic aerosols on the earth system. In this study, using the Geophysical Fluid Dynamics Laboratory's (GFDL) Atmospheric Model version 4 (AM4) model, we show that the ERF of the individual aerosol species depends upon the prescription of the emission levels of the other aerosol species. For instance, the prescription of emissions or organic carbon aerosol to PI and PD values changes the ERF of sulfate-black carbon (SBC) composite species by 37% over eastern China. This dependence principally arises from the aerosol-cloud interaction, while aerosol-radiation interactions are relatively independent of the emission levels of the other aerosol species. Nevertheless, on a global mean basis, this dependence of ERF of SBC on the emissions of other anthropogenic aerosols is much weak. The effective radiative forcing (ERF) of sulfate-black carbon (SBC) composite species in GFDL AM4 model ranges from -0.51 +/- 0.1 to -1.06 +/- 0.1 W m-2The broad range is attributed to the choice of emissions and the permitted influence of the other aerosol speciesOver East China, the choice of the emission condition for organic carbon (present-day or preindustrial) modulates the ERF of SBC by 37%

Short-lived climate pollutants (SLCPs) including methane, tropospheric ozone, and black carbon in this work, is a set of compounds with shorter lifetimes than carbon dioxide (CO2) and can cause warming effect on climate. Here, the effective radiative forcing (ERF) is estimated by using an online aerosol-climate model (BCC_AGCM2.0_CUACE/Aero); then the climate responses to SLCPs concentration changes from the pre-industrial era to the present (1850-2010) are estimated. The global annual mean ERF of SLCPs was estimated to be 0.99 [0.79-1.20] W m(-2), and led to warming effects over most parts of the globe, with the warming center (about 1.0 K increase) being located in the mid-high latitudes of the Northern Hemisphere (NH) and the ocean around Antarctica. The changes in annual mean surface air temperature (SAT) caused by SLCPs changes were more prominent in the NH [0.78 (0.62-0.94) K] than in the Southern Hemisphere [0.62 (0.45-0.74) K], and the global annual mean value is 0.70 K. By looking at other variable responses, we found that precipitation had been increased by about 0.10 mm d(-1) in mid- and high-latitudes and decreased by about 0.20 mm d(-1) in subtropical regions, with the global annual mean value of 0.02 mm d(-1). Changes in SLCPs also influenced atmospheric circulation change, a northward shift in the Intertropical Convergence Zone was induced due to the interhemispheric asymmetry in SAT. However, it is found in this work that SLCPs changes had little effect on global average cloud cover, whereas the local cloud cover changes could not be ignored, low cloud cover increase by about 2.5% over high latitudes in the NH and the ribbon area near 60 degrees S, and high cloud cover increased by more than 2.0% over northern Africa and the Indian Ocean. Finally, we compared the ERFs and global and regional warming effects of SLCPs with those induced by CO2 changes. From 1850 to the present, the ERF of SLCPs was equivalent to 66%, 83%, and 50% of that of CO2 in global, NH, and SH mean, respectively. The increases in SAT caused by SLCPs were 43% and 55% of those by CO2 over the globe and China, respectively.

This study evaluates the performance of a newly developed atmospheric chemistry-climate model, BCCAGCM_CUACE2.0 (Beijing Climate Center Atmospheric General Circulation Model_China Meteorological Administration Unified Atmospheric Chemistry Environment) model, for determining past (2010) and future (2050) tropospheric ozone (O-3) levels. The radiative forcing (RF), effective radiative forcing (ERF), and rapid adjustments (RAs, both atmospheric and cloud) due to changes in tropospheric O-3 are then simulated by using the model. The results show that the model reproduces the tropospheric O-3 distribution and the seasonal changes in O-3 surface concentration in 2010 reasonably compared with site observations throughout China. The global annual mean burden of tropospheric O-3 is simulated to have increased by 14.1 DU in 2010 relative to pre-industrial time, particularly in the Northern Hemisphere. Over the same period, tropospheric O-3 burden has increased by 21.1 DU in China, with the largest increase occurring over Southeast China. Although the simulated tropospheric O-3 burden exhibits a declining trend in global mean in the future, it increases over South Asia and Africa, according to the Representative Concentration Pathway (RCP) 4.5 and 8.5 scenarios. The global annual mean ERF of tropospheric O-3 is estimated to be 0.25 W m(-2) in 1850-2010, and it is 0.50 W m(-2) over China. The corresponding atmospheric and cloud RAs caused by the increase of tropospheric O-3 are estimated to be 0.02 and 0.03 W m(-2), respectively. Under the RCP2.6, RCP4.5, RCP6.0, and RCP8.5 scenarios, the annual mean tropospheric O-3 ERFs are projected to be 0.29 (0.24), 0.18 (0.32), 0.23 (0.32), and 0.25 (0.01) W m-2 over the globe (China), respectively.

Opposite anthropogenic aerosol emission trends in Asia can lead to different responses of the climate. Here, we examined the responses of the East Asian summer monsoon (EASM) to changes in Asian anthropogenic aerosol emissions during 2006-2014 using a global aerosol/atmospheric chemistry-climate coupled model (BCC_AGCM2.0_CUACE/Aero) with two sets of emission inventories: the Community Emissions Data System (CEDS) inventory adopted by the Coupled Model Intercomparison Project Phase 6 (CMIP6) and the inventory developed at Peking University (PKU). The changes in Asian anthropogenic aerosol emissions during 2006-2014 between the two inventories were remarkably different, particularly in eastern China where completely opposite trends were observed (i.e., increase in the CEDS inventory, but significant reduction in the PKU inventory). The perturbation simulations with the Asian anthropogenic aerosol forcing from the two inventories showed opposite changes in aerosol optical depth, aerosol effective radiative forcing, cloud liquid water path, and total cloud cover in eastern China. The simulated 'dipole-type' changes (i.e., increase in India but decrease in China) in Asian aerosols and the resulting changes in local radiation budget under the PKU inventory were consistent with the corresponding observations. The summer surface temperatures over eastern China decreased by 0-0.4 K because of the Asian anthropogenic aerosol forcing under the CEDS inventory, while they increased by 0.1-0.8 K under the PKU inventory. The weakening of the EASM index caused by the Asian aerosol forcing under the PKU inventory was twofold greater than that under the CEDS inventory (-0.4 vs. -0.2). The Asian 'dipole-type' aerosol forcing contributed to the observed summer 'southern drought and northern flood' phenomenon in eastern China during 2006-2014. The slow ocean-mediated response to the regional 'dipole-type' aerosol forcing dominated the weakening of the EASM circulation and the precipitation changes in eastern China in the total response. This study further confirms that the biases in anthropogenic aerosol emissions over Asia can affect the CMIP6-based regional climate attribution.

Estimates of the effective radiative forcing from aerosol-radiation interaction (ERFari) of anthropogenic Black Carbon (BC) have been disputable and require better constraints. Here we find a substantial decline in atmospheric absorption of -5.79Wm(-2)decade(-1) over eastern central China (ECC) responding to recent anthropogenic BC emission reductions. By combining the observational finding with advances from Coupled Model Intercomparison Project phase6 (CMIP6), we identify an emergent constraint on the ERFari of anthropogenic BC. We show that across CMIP6 models the simulated trends correlate well with simulated annual mean shortwave atmospheric absorption by anthropogenic BC over China. Making use of this emergent relationship allows us to constrain the aerosol absorption optical depth of anthropogenic BC and further provide a constrained range of 2.4-3.0 Wm(-2) for its top-of-atmosphere ERFari over China, higher than existing estimates. Our work supports a strong warming effect of BC over China, and highlights the need to improve BC simulations over source regions.

In order to quantify air pollution effects on climate change, we investigated the climate response associated with anthropogenic particulate matters (PMs) by dividing fine PM (PM2.5, particle size 2.5 mu m) in great detail in this work, with an aerosol-climate coupled model. We find that the changes in PM2.5 and CPM are very different and thus result in different, even opposite effects on climate, especially on a regional scale. The column burden of PM2.5 increases globally from 1850 to the present, especially over Asia's southern and eastern parts, whereas the column concentration of CPM increases over high-latitude regions and decreases over South Asia. The resulted global annual mean effective radiative forcing (ERF) values due to PM2.5 and CPM changes are -1.21 W center dot m(-2) and -0.24 W center dot m(-2), respectively. Increases in PM2.5 result in significant cooling effects on the climate, whereas changes in CPM produce small and even opposite effects. The global annual mean surface air temperature (SAT) decreases by 0.94 K due to PM2.5 increase. Coolings caused by increased PM2.5 are more apparent over Northern Hemisphere (NH) terrain and ocean at mid- and high latitudes. Increases in SATs caused by increased CPM are identified over high latitudes in the NH, whereas decreases are identified over mid-latitude regions. Strong cooling due to increased PM2.5 causes a southward shift of the Intertropical Convergence Zone (ITCZ), whereas the Hadley circulation associated with CPM is enhanced slightly over both hemispheres, along with the weak movement of corresponding ITCZ. The global annual mean precipitation decreases by approximately 0.11 mm day(-1) due to the increased PM2.5. Generally, PM2.5 concentration changes contribute more than 80% of the variation caused by all anthropogenic aerosols in ERF, SAT, cloud fraction, and precipitation.

Aerosol processes and, in particular, aerosol-cloud interactions cut across the traditional physical-Earth system boundary of coupled Earth system models and remain one of the key uncertainties in estimating anthropogenic radiative forcing of climate. Here we calculate the historical aerosol effective radiative forcing (ERF) in the HadGEM3-GA7 climate model in order to assess the suitability of this model for inclusion in the UK Earth system model, UKESM1. The aerosol ERF, calculated for the year 2000 relative to 1850, is large and negative in the standard GA7 model leading to an unrealistic negative total anthropogenic forcing over the twentieth century. We show how underlying assumptions and missing processes in both the physical model and aerosol parameterizations lead to this large aerosol ERF. A number of model improvements are investigated to assess their impact on the aerosol ERF. These include an improved representation of cloud droplet spectral dispersion, updates to the aerosol activation scheme, and black carbon optical properties. One of the largest contributors to the aerosol forcing uncertainty is insufficient knowledge of the preindustrial aerosol climate. We evaluate the contribution of uncertainties in the natural marine emissions of dimethyl sulfide and organic aerosol to the ERF. The combination of model improvements derived from these studies weakens the aerosol ERF by up to 50% of the original value and leads to a total anthropogenic historical forcing more in line with assessed values.

Influences of the mixing treatments of anthropogenic aerosols on their effective radiative forcing (ERF) and global aridity are evaluated by using the BCC_AGCM2.0_CUACE/Aero, an aerosol-climate online coupled model. Simulations show that the negative ERF due to external mixing (EM, a scheme in which all aerosol particles are treated as independent spheres formed by single substance) aerosols is largely reduced by the partial internal mixing (PIM, a scheme in which some of the aerosol particles are formed by one absorptive and one scattering substance) method. Compared to EM, PIM aerosols have much stronger absorptive ability and generally weaker hygroscopicity, which would lead to changes in radiative forcing, hence to climate. For the global mean values, the ERFs due to anthropogenic aerosols since the pre-industrial are-1.02 and-1.68 W m(-2) for PIM and EM schemes, respectively. The variables related to aridity such as global mean temperature, net radiation flux at the surface, and the potential evaporation capacity are all decreased by 2.18/1.61 K, 5.06/3.90 W m(-2), and 0.21/0.14 mm day(-1) since 1850 for EM and PIM schemes, respectively. According to the changes in aridity index, the anthropogenic aerosols have caused general humidification over central Asia, South America, Africa, and Australia, but great aridification over eastern China and the Tibetan Plateau since the pre-industrial in both mixing schemes. However, the aridification is considerably alleviated in China, but intensified in the Arabian Peninsula and East Africa in the PIM scheme.

We used an online aerosol-climate model (BCC_AGCM2.0_CUACE/Aero) to simulate effective radiative forcing and climate response to changes in the concentrations of short-lived climatic pollutants (SLCPs), including methane, tropospheric ozone, and black carbon, for the period 2010-2050 under Representative Concentration Pathway scenarios (RCPs) 8.5, 4.5, and 2.6. Under these three scenarios, the global annual mean effective radiative forcing were 0.1, -0.3, and -0.5Wm(-2), respectively. Under RCP 8.5, the change in SLCPs caused significant increases in surface air temperature (SAT) in middle and high latitudes of the Northern Hemisphere and significant decreases in precipitation in the Indian Peninsula and equatorial Pacific. Global mean SAT and precipitation increased by 0.13K and 0.02 mmd(-1), respectively. The reduction in SLCPs from 2010 to 2050 under RCPs 4.5 and 2.6 led to significant decreases in SAT at high latitudes in the Northern Hemisphere. Precipitation increased slightly in most continental regions, and the Intertropical Convergence Zone moved southward under both of these mitigation scenarios. Global mean SAT decreased by 0.20 and 0.44K, and global averaged precipitation decreased by 0.02 and 0.03 mmd(-1) under RCPs 4.5 and 2.6, respectively.